1. Field of the Invention
Disclosed is a self-pumping hydropneumatic spring strut with internal leveling control, particularly for motor vehicles.
2. Description of the Related Art
Spring struts in which the high-pressure chamber is connected to a flow connection arranged in the piston rod guide are known, e.g., DE 101 04 358 C1, FIG. 7 and FIG. 8. A fill hole, arranged in the outer tube, communicates with a flow connection in the incompletely assembled state of the piston rod guide. The fill hole is closed by the piston rod guide after the piston rod guide is inserted axially into the outer tube. A closed sleeve body whose shape can be changed and whose wall comprises a gastight barrier layer is provided as a high-pressure chamber. This design is advantageous for several reasons. The necessary internal parts such as the high-pressure chamber, the piston, the piston rod and the pump rod together with the piston rod guide, are inserted axially into the outer tube of the spring strut. Second, the spring strut is operational after filling at least the high-pressure chamber with pressure gas through the fill hole. Third, the fill hole is closed by the piston rod guide after the piston rod guide along with the work cylinder and the rest of the internal parts, are pushed in further axially so that the spring strut is completely assembled after flanging the outer tube.
In order to ensure axial insertion of the piston rod guide, it is necessary that the seal is arranged between the piston rod guide and the piston rod so as to be pretensioned. This results in a correspondingly high friction. An individual seal of this kind under such high stress tends to leak toward the atmosphere because the internal pressure must be entirely contained by this seal.